firmware-utils: add new tool tplink-safeloader for the new TP-LINK Pharos devices (CPE210/220/510/520)

The new TP-LINK Pharos series uses a new bootloader, the "TP-LINK Safeloader".
It uses an advanced firmware image format, containing an image partition table
and a flash partition table (and image partitions are mapped to the
corresponding flash partitions). The exact image format is documented in the
source code.

Furthermore, the bootloader expects the kernel image as an ELF executable.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43384 3c298f89-4303-0410-b956-a3cf2f4a3e73